Objective     To explore the effect of low-dose cyclophosphamide (CTX)on apoptosis of implanted human lung carcinoma in nude mice.      Methods     BALB／c nude mice bearing lung carcinoma were randomized into several groups，each receiving different dose of CTX respectively. We investigated antitumor effect and toxicity of CTX. At the end of experiment， tumors were resected for immunohistochemical staining. Nuclear factor κB (NF-κB P65)was detected and apoptosis was measured by TUNEL. Morphological changes of tumor cells were observed.      Results     The volume of tumors was much smaller in mice receiving continuous low-dose CTX than that receiving maximally tolerated dose of CTX and normal saline (control group). The apoptotic index was increased and NF-κB P65 decreased in the mice receiving low-dose of CTX.      Conclusion     The continuous low-dose of CTX inhibits the growth of implanted tumor and increases tumor cell apoptosis，which may be due to the down-regulation of nuclear factor κB.